Commitments and Contingencies - Casualty loss and environmental matters (Details) - Washington [Member] - Medical Office Building [Member] - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Liability related to an environmental concern		$ 1,200,000
Remediation funded during period	$ 0.3

Cost incurred in providing environmental engineering and consulting; environmental testing and analysis; and remediation services during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_CostOfServicesEnvironmentalRemediation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration